E85 for Performance Tuning

When it comes to extracting maximum power from a turbocharged engine or high-compression build, few fuel choices generate as much discussion—and results—as E85. This ethanol-based fuel has become a staple in the performance community, from weekend warriors to professional race teams. But E85 isn’t a magic bullet, and understanding when it makes sense, what it requires, and which platforms benefit most can mean the difference between a reliable power gain and an expensive lesson.

What Is E85?

E85 is a fuel blend consisting of approximately 85% ethanol and 15% gasoline. The “85” in the name refers to the ethanol percentage, though it’s important to note that pump E85 can legally contain anywhere from 51% to 83% ethanol depending on the season and location. Winter blends often drop to 60-70% ethanol to improve cold-start performance in freezing temperatures. For a complete dive into “What Is E85”, see our full post.

The key characteristic that makes E85 attractive to tuners is its octane rating. While pump premium gasoline typically rates at 91-93 octane, E85 delivers an effective octane rating of 100-105, putting it on par with expensive race fuels at a fraction of the cost.

Why Performance Enthusiasts Choose E85

Superior Knock Resistance

The high knock resistance of E85 allows tuners to push more boost, increase compression ratios, and run more aggressive ignition timing curves without risking engine damage. This is especially valuable in turbocharged and supercharged applications where detonation becomes a limiting factor as power increases.

Natural Cooling Effect

Ethanol absorbs more heat during vaporization, which keeps intake temperatures low and reduces the risk of detonation. Lower intake air temperatures translate directly to denser air charges and more power potential, particularly important for forced induction setups.

Real-World Power Gains

The performance gains from E85 vary significantly based on the engine configuration:

Naturally Aspirated Engines: Well-executed E85 tuning typically yields 5-15% horsepower gains for naturally aspirated engines. While not as dramatic as boosted applications, this represents a meaningful improvement for builds that have maxed out other modifications.

Turbocharged and Supercharged Engines: This is where E85 truly shines. Turbo or supercharged builds commonly see 15-25% power increases, with some configurations gaining even more. Many turbo builds experience 50+ horsepower gains when properly switching and tuning for E85.

Cost Advantage

E85 is often cheaper than premium gasoline, and it certainly costs far less than race fuels with comparable octane ratings. For racers and enthusiasts running high-performance engines regularly, the cost savings can be substantial over time.

Which Platforms Benefit Most From E85?

Common Candidates for E85 Conversion

Turbocharged Vehicles: E85 is particularly effective for high horsepower or high compression builds, especially those with forced induction. Platforms like:

• Subaru WRX and STI (EJ and FA engines)
• Mitsubishi Evolution
• Mazda Miata with turbo kits
• BMW N54/N55 twin-turbo models
• Volkswagen GTI and Golf R

Supercharged Applications: Upgraded turbos or superchargers pair perfectly with E85, with many turbo builds seeing 50+ horsepower gains when switching and tuning properly. Popular platforms include:

• Ford Mustang GT (Coyote and older 5.0L engines)
• Chevrolet Corvette and Camaro
• Dodge Challenger and Charger (Hellcat and Scat Pack)

High-Compression Naturally Aspirated Builds: For vehicles with compression ratios over 11:1 or 12:1, E85 represents an excellent choice. This includes:

• Honda Civic Type R and Si
• Toyota 86/Subaru BRZ with built engines
• Mazda MX-5 with high-compression builds

Less Suitable Applications

Someone running lower compression ratios on a naturally aspirated engine would see some small benefits with E85, but not enough to justify the added fuel consumption. Stock or mildly modified vehicles without boost or high compression typically don’t realize sufficient gains to offset the drawbacks.

Essential Fuel System Requirements

Converting to E85 isn’t as simple as filling up at a different pump. The increased fuel volume demands and ethanol’s corrosive properties require specific upgrades.

Fuel Injectors

E85’s lower energy density requires 30-40% increased flow from the fuel system to maintain proper air-fuel ratios. This means:

• **30-40% larger injectors** than what you’d run for the same power level on gasoline
• Injector internals must be made of stainless steel or materials resistant to corrosion and water
• Modern injectors like Bosch EV14 series work well with E85

Fuel Pumps

E85 requires the fuel system to supply 35% more fuel for a given horsepower level, meaning the pump must support this increased volume. Requirements include:

• Brushless fuel pumps are the most durable choice for E85, though quality brushed pumps with carbon commutators can work well
• Avoid pumps with copper commutators
• Consider upgrading from a typical 255 LPH pump to 400+ LPH for higher power applications

Fuel Lines and Fittings

It’s recommended to use CPE synthetic rubber line for concentrations up to 85% ethanol and PTFE (Teflon) lines for concentrations above 85%. Material compatibility is critical:

• Replace OEM rubber lines with E85-compatible materials
• Use stainless steel or anodized aluminum fittings
• Viton O-rings are the best choice for use with E85
• Hard lines from 2001+ vehicles are typically acceptable

Fuel Filters and Regulators

• 10-micron filtration is required for proper injector protection—never increase filter pore size despite misconceptions
• Stainless mesh filters work best
• Pressure regulators should have stainless internals and fiber-reinforced Viton diaphragms

Tuning Requirements and Methods

Fixed E85 Tune

The simplest but least flexible approach. An E85 tune commands the engine to deliver much more fuel per injection cycle and is designed for one fuel only: 85% ethanol fuel. This works for dedicated race cars but isn’t practical for street use.

Pros: Straightforward, no additional sensors needed

Cons: Can’t run gasoline, vulnerable to ethanol content variations

Flex Fuel Systems

Modern flex fuel systems represent the gold standard. Adaptive flex fuel systems from companies like Advanced Fuel Dynamics work in real-time, allowing you to fill up with gas or E85 anytime and drive immediately. These systems use ethanol content sensors to continuously monitor the fuel composition and adjust the engine management accordingly.

Popular systems include:

• COBB Accessport with flex fuel kit (Subaru, Volkswagen)
• ProFlex Commander (Ford Mustang, various platforms)
• Haltech and AEM standalone ECUs with flex fuel capability

Custom Dyno Tuning

Tuning for E85 entails putting your car on a dyno and fine-tuning the engine management computer to maximize results. Professional tuning is essential because:

• Air-fuel ratios differ significantly from gasoline
• Ignition timing can be advanced considerably
• Cold start and warm-up parameters need adjustment
• Boost levels can be safely increased

The Drawbacks: What You Need to Know

Fuel Availability

E85 is not readily available across the entire country, making it better suited for people who remain local. Before committing to E85, find E85 gas stations near you, to make sure there’s a convenient source nearby.

Reduced Fuel Economy

E85 has roughly 75% of the energy content of gasoline, reducing vehicle range by approximately 25%. That 300-mile tank on premium gas becomes 225 miles on E85. For daily drivers, this means more frequent fill-ups.

Fuel Consistency Issues

The actual ethanol content in pump E85 can legally be as low as 51%, leading to wild swings in fuel consistency from tank to tank. This variability makes flex fuel systems nearly mandatory for pump E85 users.

Cold Weather Challenges

Ethanol is not as easy to ignite when mixed with cold air and sprayed into a cold cylinder, which can make cold starts difficult in freezing temperatures. Proper tuning for cold weather operation is essential.

Moisture Attraction

E85 is hygroscopic, meaning it attracts moisture from its surroundings. Long-term storage with E85 in the tank can lead to corrosion issues. Many experts recommend flushing the system and running gasoline if the vehicle will sit for extended periods.

Making the Decision: Is E85 Right for You?

E85 Makes Sense If:

• **You have forced induction or high compression** – The power gains justify the investment
• **E85 is readily available locally** – Multiple stations in your area make refueling convenient
• **You’re primarily focused on performance** – The reduced range isn’t a dealbreaker
• **You have the budget for proper fuel system upgrades** – Cutting corners on E85 conversions leads to problems
• **You’re willing to invest in a flex fuel system or dedicated tune** – Proper tuning is non-negotiable

Skip E85 If:

• **Your engine is stock or mildly modified** – The gains won’t justify the costs
• **E85 isn’t available in your area** – Road trips become complicated
• **You need maximum fuel economy** – The 25% reduction in range matters for your use case
• **You can’t invest in proper fuel system upgrades** – Half measures lead to failures

Real-World Example: The Numbers Don’t Lie

A Mazda Miata with a forged 1.6L engine and GTX2867R Gen II turbo was tested on both pump gas and E85 on the same dyno, with the same tuner. The E85 tune delivered measurably more power across the entire RPM range with the ability to run more boost and advanced timing safely.

Testing a 2013 Camaro ZL1 with a supercharged LT4 engine showed 600 horsepower on pump E85, then jumped to 644 horsepower and 668 lb-ft of torque when switched to VP Racing’s C85 race-grade ethanol and properly tuned. The engine safely absorbed two to three additional degrees of timing with the consistent ethanol content.

Best Practices for E85 Users

• **Test your fuel** – Use an E85 test kit to verify ethanol content, especially at new stations
• **Monitor air-fuel ratios** – Install a wideband O2 sensor for real-time monitoring
• **Keep multiple tunes** – Have both E85 and 93-octane maps available for flexibility
• **Maintain your fuel system** – Run gasoline periodically to lubricate components
• **Plan your routes** – Know where E85 stations are located for road trips
• **Invest in quality components** – Cheap fuel system parts will fail with E85

Conclusion

E85 isn’t just a fueling decision—it supercharges everything, especially when paired with high-end hardware and proper tuning. For turbocharged and supercharged builds, the power gains, knock resistance, and cooling benefits make E85 an excellent choice when implemented correctly.

However, success with E85 demands respect for its requirements. Proper fuel system upgrades, professional tuning, attention to fuel quality, and realistic expectations about availability and fuel economy separate successful E85 conversions from expensive failures.

Whether you’re building a dedicated track car, a street/strip monster, or a high-horsepower daily driver, E85 offers race fuel performance at pump gas prices—but only when you’re willing to do it right.